Okay! Following your previous schematic post, I tested : Red & Gray, then Yellow & Black
These terminals, tested by oscilloscope, produced a ~3v AC.
I guess that's a problem!
Edit: But checking the schematicbit looks like the test below is correct: red&black, yellow&gray, but the schematic just shows 0.5A AC, it doesn't show voltage.
By myself, I had tested this way (Red & Black, then Gray & Yellow) which produced a 30v AC somewhat flattened sine wave on the scope.
That made me think the transformer was okay, but if those are not the right terminals to test, then it's a problem.
I'll have to remove the diodes for testing after work tonight.